ConchoidalArthur Thomas, Gemstones (2009), ConchoidalArthur Thomas, Gemstones (2009), Brittle, Conchoidal
UnevenArthur Thomas, Gemstones (2009), UnevenArthur Thomas, Gemstones (2009), Uneven
ZrO 2Arthur Thomas , Gemstones (2009)
FeS 2Michael OâDonoghue , Gems, Sixth Edition (2006) More from other references